Binary Stars May be Likely to Harbor Life, After All

Young stars face a harsh life within the stellar nurseries in which they are formed, as stellar bodies make close passes to each other, just as planets are starting to develop. However, new research shows this process may make the rise of life on these worlds more likely.

The habitable zone surrounding a star is sometimes known as the “Goldilocks zone,” where temperatures are neither too hot nor too cold for liquid water to form on their surface. Water, necessary for life as we know it to exist, could make the development of life on other worlds more likely. As stars pass by pairs of binary stars, gravity can draw these bonded pairs of stars closer to each other, increasing the size the habitable zone, making life in the system more apt to develop, this new research reveals.

“Our model suggests that there are more binary systems where planets sit in Goldilocks zones than we thought, increasing the prospects for life. So those worlds beloved of science fiction writers — where two suns shine in their skies above alien life — look a lot more likely now,” said Bethany Wootton, who carried out the work while an undergraduate researcher in astronomy at the University of Sheffield.

An artist’s conception of a world, orbiting in a binary star system, teeming with life. Image credit: Mark Garlick

University of Sheffield researchers utilized computer simulations to show how young stars are affected by the gravity of neighboring systems in stellar nurseries. They found that binary stars can be drawn closer together by the passing of other stars, increasing the size of their habitable zones. In a typical cluster containing 350 binary systems, this effect could affect up to 20 such systems, researchers found. In some cases, the habitable zones around each star can overlap, further increasing the chances of life on worlds in such a system.

A planet and moon form around a binary star system within a nebula in this artist concept of a young solar system. Image credit: Matt Hendrick/Flickr

Approximately one-third of all stars in the galaxy are found in systems containing two or more stars, and this percentage is higher among young stars. Some pairs orbit so close to each other they share material between them, while others are separated by thousands of astronomical units (one astronomical unit, or AU, is the average distance between the Earth and Sun). Many stars are also partnered with more than one other star in triple systems (or more!).

The gravitational fields in systems with multiple stars can pose havoc with planets that orbit too far from their parent stars. However, planetary orbits can remain stable, provided the planets reside close enough to their sun.

“As long as the planet orbits one of the stars at less than one-third of the distance between the two stars, it will have a stable long term orbit in the binary. An interaction that pushes the stars closer together will restrict the orbits a planet can have, but there will still be locations (including in the habitable zone) where the planet will be stable,” said Dr. Richard Parker, also of the University of Sheffield.

When stars in multiple star systems orbit far from each other, their habitable zones are found around each stellar body. However, in systems where pairs of stars are close to each other, warmth from each star contributes to the size of the Goldilocks zone, increasing the chances for life on worlds surrounding these stars.

Life is most likely to form on planets which are within the habitable zone from their sun — making them neither too hot nor too cold for liquid water to pool on their surface. Image credit: NASA

Just 35 years ago, astronomers did not know of any planets outside our Solar System. Now, more than 3,000 exoplanets have been found orbiting other stars. In 2012, multiple planets were found in a binary system for the first time, using the Kepler spacecraft.

“Unlike our sun, many stars are part of multiple-star systems where two or more stars orbit one another. The question always has been — do they have planets and planetary systems? In our search for habitable planets, we have found more opportunities for life to exist,” said William Borucki, Kepler mission principal investigator at NASA’s Ames Research Center, following the Kepler discovery.

Much like the desert world of Tatooine in Star Wars, any lifeforms on planets surrounding binary stars would experience day and night in a different way than we do on Earth.

“The main difference is that you would have two ‘Suns’ in the sky. So, you would have two sunrises, two sunsets, etc. However, each star wouldn’t necessarily have to rise and set at a similar time to the other, which would result in different length days,” Wootton explains, in an exclusive interview with The Cosmic Companion.

The Transiting Exoplanet Survey Satellite (TESS) spacecraft, launched in April 2018, will examine the sky in search of exoplanets, taking over where the Kepler mission ended. However, it will be unable to answer the pivotal question related to this latest research.

“Kepler has already detected planets in the habitable zone around stars, and it has discovered planets orbiting binary stars. Missions like TESS will discover many more planets, but we wont be able to tell if the host stars have been pushed closer together by an interaction in the past,” Dr. Parker tells The Cosmic Companion.

Our own Sun may have been born close to the site of an ancient supernova explosion. Such an occurrence would be disastrous to life on Earth today, but this event may have led to internal heating in the Earth, which proved vital to the development and evolution of life on our planet. Research will continue on the lives of young stars, in an effort to understand if similar dramatic events happening to young stars can increase the chances for the formation of life.